1. Field of the Invention
The present invention relates to an air bearing slider for a disk drive, and more particularly, to an air bearing slider for a disk drive which can minimize the lowering of the flying height due to differences in elevations or altitudes.
2. Description of the Related Art
A disk drive, for example, a hard disk drive (HDD), is one of many auxiliary memory devices of a computer that is used to record data on the disk or reproduce stored data from the disk by using a read/write head.
FIG. 1 is a perspective view illustrating part of a typical hard disk drive. Referring to FIG. 1, a typical hard disk drive includes a magnetic disk (hard disk) 10 which is a recording medium for data recording, a spindle motor 20 for rotating the disk 10, a read/write head 31 for recording data on the disk 10 or reproducing data stored on the disk 10, and an actuator 30 for moving the read/write head 31 to a predetermined position on the disk 10.
The actuator 30 includes an actuator arm 36 rotated by a voice coil motor (not shown), an air bearing slider 32 where the read/write head 31 is mounted, and a suspension 34 installed at one end portion of the actuator arm 36 and supporting the air bearing slider 32 to be elastically biased toward a surface of the disk 10. The air bearing slider 32 having the read/write head 31 is lifted to a predetermined height above the disk 10 to maintain a predetermined gap between the read/write head 31 and the disk 10.
When the rotation of the disk 10 is stopped, the slider 32 is parked in a landing zone 11 provided on a surface of an inner circumferential side of the disk 10. However, as the disk 10 starts to rotate, a lifting force generated by airflow applies to a lower surface of the slider 32, that is, to an air-bearing surface, thus lifting the slider 32. The slider 32 is lifted to a height where a lifting force created by the rotation of the disk 10 and an elastic force created by the suspension 34 are balanced. The slider 32 in a lifted state is moved to a data zone 12 of the disk 10 according to a rotation of the actuator arm 36. The read/write head 31 mounted on the slider 32 records and reproduces data from the disk 10 while maintaining a predetermined gap with the rotating disk 10.
The air bearing slider described above has a variety of structures. An example thereof, is the basic structure of a conventional TF (taper flat) type air bearing slider illustrated in FIG. 2.
Referring to FIG. 2, a TF type air bearing slider 40 has a body 42 having a thin block shape. Two rails 44 extending in a lengthwise direction of the body 42 are formed to a predetermined height on one surface of the body 42, that is, on a surface facing the disk. An inclined surface 46 is formed at a leading end portion of each of the rails 44. In the above structure, when air flow is created in a direction indicated by an arrow A by the rotation of the disk, air is compressed on the inclined surface 46, thus applying positive pressure to the surface of each of the rails 44, and creating a lifting force which lifts the slider 40 above the surface of the disk.
However, in the TF type air bearing slider 40, the lifting force gradually increases as the rpm of the disk increase, gradually increasing the flying height. The rpm of a disk and the flying height are almost linearly proportional.
In the meantime, an NP (negative pressure) type air bearing slider which can maintain a constant flying height by generating a negative pressure as well as pulling the slider toward a surface of a disk is increasingly adopted. FIG. 3 shows a basic structure of a conventional NP type air bearing slider.
Referring to FIG. 3, two rails 54 extending in a lengthwise direction of a body 52 of an NP type air bearing slider 50 are formed on one surface of the body 52, that is, a surface facing a disk (not shown). A cross rail 58 extending in a widthwise direction of the body 52 is formed between the rails 54. An inclined surface 56 is formed at a leading end portion of each of the rails 54. The cross rail 58 is formed to have the same height as of the rails 54. In the above structure, when air flow is created by rotation of the disk in a direction indicated by an arrow A, the two rails 54 generate positive pressure at both side portions of the body 52 and the cross rail 58 generates a negative pressure cavity 59 at the central portion of the body 52. At the initial stage of the disk rotation, since the positive pressure is higher than the negative pressure, the slider 50 is lifted. As the speed of rotation of a disk increases, the negative pressure gradually increases. When the disk rotation speed reaches a regular rpm, the positive pressure and the negative pressure are balanced so that the slider 50 is no longer lifted and maintained at a constant flying height.
Forces acting on the above NP type air bearing slider are described in detail with reference to FIG. 4.
Referring to FIG. 4, when a disk 10 rotates in a direction indicated by an arrow D, air flow is formed in a direction indicated by an arrow A between the disk 10 and a surface of a slider 60 facing the disk 10, that is, an air bearing surface. Positive pressure is generated by the airflow on a surface of rails 64 protruding from a low surface of the slider 60, that is, on the air-bearing surface. Accordingly, lifting forces F1 and F2, which lift the slider 60, are generated. In contrast, negative pressure or sub-ambient pressure is generated at a negative pressure cavity 69 of the slider 60 so that a force F3 pulling the slider 60 toward the disk 10 is also generated. In the meantime, gram load F4 by suspension (refer to FIG. 1) acts on the slider 60. As a result, the slider 60 is maintained at a height at which the forces F1, F2, and F3 generated by the above-described positive and negative pressures and the gram load F4 are balanced. As the negative pressure increases, the positive pressure must also increase in order to maintain a balanced state. When the positive pressure and the negative pressure increase in a balanced state, air-bearing stiffness of the slider increases improving dynamic stability.
FIG. 5 shows a detailed example of the conventional NP type air bearing slider, which is disclosed in U.S. Pat. No. 5,309,303.
Referring to FIG. 5, an inclined surface 71 and a cross rail 72 are formed at a leading end portion of a slider 70. Two side rails 73 are formed at both side portions of the slider 70. An island 77 supporting a head 78 protrudes at a tailing end portion of the slider 70. A negative pressure cavity 76 defined by the cross rail 72 and the side rails 73 is formed at the central portion of the slider 70. A first groove 74 connecting the negative pressure cavity 76 and the outside of the slider 70 is formed at the leading end portion of each of the side rails 73 across the side rails 73. The first groove 74 is inclined with respect to a lengthwise axis of the slider 70 and has the same depth as the negative pressure cavity 76. The first groove 74 has a function of maintaining a gap between each of the side rails 73 and a disk (not shown) to be identical.
Also, a second groove 75 is formed at the tailing end portion of each of the side rails 73. The second groove 75 is open at the side surface edge of each of the side rails 73, but is separated from the negative pressure cavity 76. The second groove 75 has the same depth as the negative pressure cavity 76 and is inclined with respect to a lengthwise axis of the slider 70 to prevent debris from remaining therein. The second groove 75 generates negative pressure at the tailing end portions of the side rails 73 so that the flying height of the slider 70 can be lowered. Thus, according to the structure of the slider 70 shown in FIG. 5, a lower flying height can be obtained, thereby improving the performance of the head 78.
However, in the above-described conventional air bearing sliders, as altitude or elevation increases, flying height is generally lowered. This problem will now be described with reference to FIGS. 6A and 6B.
Referring to FIG. 6A, when the absolute altitude or elevation is 0 m, a slider 80 maintains a predetermined flying height H1, for example, a flying height of 10 nm, above the disk 10 rotating at a regular rpm. The slider 80 is maintained in an inclined state at a predetermined angle as the leading end portion where air enters is lifted higher than the trailing end portion where a head 81 is disposed. The flying height H1 signifies a gap between the trailing end portion of the slider 80 and the disk 10.
However, as the absolute altitude increases, the atmospheric pressure is lowered. Accordingly, the flying height of the conventional air bearing slider 80 is generally lowered due to a decrease in a lifting force. As shown in FIG. 6B, the flying height H2 of the slider 80 at a place where the absolute altitude is about 3,000 m is about 7 nm, which is 30% less than the flying height H1 at the place where the absolute altitude is 0 m. When the flying height of the slider 80 is lowered as the altitude increases, the head 81 easily contacts the disk 10 by a relatively weak impact or vibration. Accordingly, the head 81 is damaged and the lift span is reduced, deteriorating the reliability of a disk drive. In particular, since a lower flying height is needed to improve performance of the head as described above, the lowering of the slider according to the altitude becomes a serious problem.